Purification and Characterization of Aspergillus terreus α-Galactosidases and Their Use for Hydrolysis of Soymilk Oligosaccharides

alpha-Galactosidases has the potential to hydrolyze alpha-1-6 linkages in raffinose family oligosaccharides (RFO). Aspergillus terreus cells cultivated on wheat bran produced three extracellular forms of alpha-galactosidases (E1, E2, and E3). E1 and E2 alpha-galactosidases presented maximal activities at pH 5, while E3 alpha-galactosidase was more active at pH 5.5. The E1 and E2 enzymes showed stability for 6 h at pH 4-7. Maximal activities were determined at 60, 55, and 50A degrees C, for E1, E2, and E3 alpha-galactosidase, respectively. E2 alpha-galactosidase retained 90% of its initial activity after 70 h at 50A degrees C. The enzymes hydrolyzed rho NPGal, melibiose, raffinose and stachyose, and E1 and E2 enzymes were able to hydrolyze guar gum and locust bean gum substrates. E1 and E3 alpha-galactosidases were completely inhibited by Hg2+, Ag+, and Cu2+. The treatment of RFO present in soy milk with the enzymes showed that E1 alpha-galactosidase reduced the stachyose content to zero after 12 h of reaction, while E2 promoted total hydrolysis of raffinose. The complete removal of the oligosaccharides in soy milk could be reached by synergistic action of both enzymes.